Martin Postma

The Marine Mammal Programme at the Prince Edward Islands: 38 years of research

The Marine Mammal Programme (MMP) conducts research on pinnipeds and killer whales Orcinus orca at Marion Island, Prince Edward Islands, under the auspices of the Mammal Research Institute, Department of Zoology and Entomology, University of Pretoria. The history of the MMP, which has benefited from collaboration with leading national and international researchers, is described from its start through to current research. The setting up of long-term studies such as the mark-resighting of southern elephant seals Mirounga leonina commenced in 1983. The elephant seal population declined by 87% between an initial census in 1951 and 2004. This was followed by a stabilisation period and a current increase. The recovery, and subsequent increase of sympatric populations of Subantarctic fur seals Arctocephalus tropicalis and Antarctic fur seals A. gazella (following cessation of commercial sealing), are documented. Insights into many aspects of elephant seal and fur seal biology, including life history, demography, diet, growth, foraging and ranging behaviour are described. Ancillary work on morphology, genetics, anthropogenic influences and rare events are mentioned, as well as the extent of current research that addresses population dynamics in an ecosystem context. Opportunistic photographic identification of killer whales and recent dedicated observations at Marion Island are used to determine population size, seasonal abundance and sociality of this population, and to further understanding of its potential impact on resident pinniped populations.

Spatial variation in female southern elephant seal mass change assessed by an accurate non-invasive photogrammetry method

Abstract Physically weighing large marine mammals sequentially over time has presented researchers with a logistical challenge and has severely limited sample sizes. Using a well-established photogrammetry method we developed a simple mathematical method to calculate accurate mass measurements at specific stages in the life cycle of a top marine predator. Female southern elephant seals (n = 23) at Marion Island were sampled sequentially using photogrammetry and three-dimensional models (based on each photogrammetry project) were built for estimation of body mass. Simple equations were applied to obtain mass at critical instances in their life cycle. Marion Island elephant seal mass data was compared to data obtained from physically weighed elephant seals from King George, South Georgia and Macquarie islands. Females from Marion Island are smaller, but their percentage lactation mass loss is similar to females from these other populations. The similarity of percentage mass loss during lactation between different female populations illustrates the accuracy and practicality of the photogrammetric method over a temporal scale. Photogrammetric mass estimation can be used alongside datasets of physically weighed animals and can greatly benefit ecology and life history studies.

First confirmed record of a leucistic Antarctic fur seal pup born outside the Scotia Arc Islands

A leucistic Antarctic fur seal (Arctocephalus gazella) pup was born on subantarctic Marion Island during the austral summer of 2010/2011. This is the first confirmed record of a leucistic fur seal pup born outside the Scotia Arc islands. Additionally, we report on a leucistic adult female Antarctic fur seal producing typical black pups for five non-consecutive summers on Marion Island. The birth of a leucistic pup, together with the multiple black pups produced by the leucistic female, suggests that the recessive genes responsible for leucism are now entrenched within the Marion Island population.

Inshore Occurrence of Southern Right Whales (Eubalaena australis) at Subantarctic Marion Island

Opportunistic shore-based sightings of southern right whales Eubalaena australis for Marion Island (46°54′S, 37°45′E) were documented at five different times between 1974 and 2009. Whales were sighted between May and September and exclusively on the eastern lee side of the Island. Notwithstanding some observer biases over this time frame, the species appears to be an infrequent visitor to the inshore marine environment of Marion Island.

Oedipus complex in an Antarctic fur seal pup

We present the first evidence of a possible case of the Oedipus complex in a non-primate. An Antarctic fur seal pup, Arctocephalus gazella, unsuccessfully directed what appeared to be copulatory behaviour towards its own mother on several occasions. A herding sub-adult bull chased the pup from the female, which strengthens our suggestion that it was copulatory behaviour we witnessed. This seemed to constitute innocent sexual play with elements of the Oedipus complex rather than coercion because the female was not stressed nor did the pup possess the physical strength to coerce the female.

Opportunistic ship-based census of pack ice seals in eastern Weddell Sea, Antarctica

The distribution, density and percentage contribution of pack ice pinnipeds during ship-board censuses in the eastern Weddell Sea in summer 2015/2016 are presented. Of the four true pack ice seal species encountered, crabeater seals predominated. Despite the low survey effort, Ross seals continued to be relatively abundant in the pack ice off the Princess Martha Coast in mid-January 2016, similar to the situation here in the 1970s. Censusing of Ross seals is ideally carried out in late January/early February when the species’ haulout probability is at its maximum and the seals are gathered in the limited summer pack ice to moult.

Hitchhiking goose barnacles and their potential implications on the functioning of animal-borne instruments

Goose barnacles (Lepas australis) were found attached to satellite-tracking and time-depth recording (TDR) instruments carried by two lactating Subantarctic fur seals (Arctocephalus tropicalis) from Marion Island. We report on the movements of these seals, both of which crossed the Subantarctic Front. Barnacles surrounding the temperature probe of one TDR device did not appear to directly influence temperature recordings, although disturbances to recording accuracies by other high-precision devices carrying goose barnacles are considered likely.